In traditional semiconductor manufacturing, integrated circuits (IC) have been built in a planar fashion, with a single layer of transistors. New developments in semiconductor manufacturing allow wafers to be vertically stacked. Vertically integrated circuits refer to semiconductor circuits produced by traditional planar technology which are disposed vertically one above the other in several levels, resulting in three-dimensional integrated circuits. This allows integrated circuits to have a higher device density and a smaller chip area.
Three-dimensional integrated circuits typically contain multiple conductive layers separated by one or more dielectric layers. Contact structures disposed in via openings in the dielectric layers provide conductive paths so that electrical signals can pass from one conductive layer to another conductive layer.
FIGS. 1A and 1B illustrate a side view and a top view of a prior art contact stricture in one layer of a three-dimensional integrated circuits respectively. A through-substrate-via (TSV) 110 is built in a substrate 100 to provide a vertical connection to another layer, and a plurality of contact structures 120 are overlaid the top surface of the TSV 110, which can be electrically connected to devices built above the substrate 100 through a metal line 130. At present, since no special contact structure design is applied for 3D TSV wafers, the size, shape, and the configuration of the contact structures 120 follow the design rule of the traditional planar process, as shown in FIG. 1B. Therefore, the process window of contact etching may be limited. In addition, the electrical flow defined in the traditional design rule is usually much smaller than the electrical flow passing through the TSV 110. Therefore, the electrical flow of three-dimensional IC will be limited, and there may be a possible electromigration (EM) issue at contact interfaces, which will limit product types.
Accordingly, as designs move to three dimensions, a new contact structure is required to solve the aforementioned problems.